Th2O-, Th2Au-, and Th2AuO1,2- Anions: Photoelectron Spectroscopic and Computational Characterization of Energetics and Bonding

Electronic Structure and Anion Photoelectron Spectroscopy of Uranium-Gold Clusters UAun-, n = 3-7

A collaborative effort between experiment and theory toward elucidating the electronic and molecular structures of uranium-gold clusters is presented. Anion photoelectron spectra of UAun-(n = 3-7) were taken at the third (355 nm) and fourth (266 nm) harmonics of a Nd:YAG laser, as well as excimer (ArF 193 nm) photon energies, where the experimental adiabatic electron affinities and vertical detachment energies values were measured. Complementary first-principles calculations were subsequently carried out to corroborate experimentally determined electron detachment energies and to determine the geometry and electronic structure for each cluster. Except for the ring-like neutral isomer of UAu6 where one unpaired electron is spread over the Au atoms, all other neutral and anionic UAun clusters (n = 3-7) were calculated to possess open-shell electrons with the unpaired electrons localized on the central U atom. The smaller clusters closely resemble the analogous UFn species, but significant deviations are seen starting with UAu5 where a competition between U-Au and Au-Au bonding begins to become apparent. The UAu6 system appears to mark a transition where Au-Au interactions begin to dominate, where both a ring-like and two heavily distorted octahedral structures around the central U atom are calculated to be nearly isoenergetic. With UAu7, only ring-like structures are calculated. Overall, the calculated electron detachment energies are in good agreement with the experimental values.

Reactions of Thorium Oxide Clusters with Water: The Effects of Oxygen Content

Thorium oxide has many important applications in industry. In this article, theoretical calculations have been carried out to explore the hydrolysis reactions of the ThO_n (n=1-3) clusters. The reaction mechanisms of the O-deficient ThO and the O-rich ThO₃ are compared with the stoichiometric ThO₂ . The theoretical results show good agreement with the prior experiments. It is shown that the hydrolysis mainly occurred on the singlet potential surface. The overall reactions consist of two hydrolysis steps which are all favourable in energy. The effects of oxygen content on the hydrolysis are elucidated. Interestingly, among them, the peroxo group O₂ ^2- in ThO₃ is converted to the HOO- ligand, behaving like the terminal O^2- in the hydrolysis which is transformed into the HO- groups. In addition, natural bond orbital (NBO) analyses were employed to further understand the bonding of the pertinent species and to interpret the differences in hydrolysis.

Protactinium and Actinium Monohydrides: A Theoretical Study on Their Spectroscopic and Thermodynamic Properties

Spectroscopic and thermodynamics properties including bond dissociation energies (BDEs), adiabatic electron affinities (AEAs), and ionization energies (IEs) have been predicted for AcH and PaH using the Feller-Peterson-Dixon composite approach. Comparisons with previous studies on ThH and UH were performed to identify possible trends in the actinide series. Multireference CASPT2 calculations were used to predict the spin-orbit effects and obtain potential energy curves for the low-lying Ω states around the equilibrium distance as well as the vertical detachment energies (VDEs) from AcH^- and PaH^- to excited states of the neutral species. The calculated AEA for AnH (An = Ac, Th, Pa, U) showed that the AEA increases from AcH (0.425 eV) to ThH (0.820 eV) and decreases to PaH (0.781 eV) and to UH (0.457 eV), whereas the IE values are 5.887 eV (AcH), 6.181 eV (ThH), 6.204 eV (PaH), and 6.182 eV (UH). The ground state of AcH, AcH^-, PaH, and PaH^- are predicted to be¹Σ⁺₀,²Π_3/2, ³H₄, and ⁴I_9/2, respectively. The BDEs for AcH and PaH are 276.4 and 237.2 kJ/mol, and those for AcH^- and PaH^- are 242.8 and 239.8 kJ/mol, respectively. The natural bond analysis shows a significant ionic character, An⁺H^-, in the bonding of the neutral hydrides.

Experimental and Computational Description of the Interaction of H and H- with U

The results of ab initio correlated molecular orbital theory electronic structure calculations for low-lying electronic states are presented for UH and UH^- and compared to photoelectron spectroscopy measurements. The calculations were performed at the CCSD(T)/CBS and multireference CASPT2 including spin-orbit effects by the state interacting approach levels. The ground states of UH and UH^- are predicted to be ⁴Ι_9/2 and ⁵Λ₆, respectively. The spectroscopic parameters T_e, r_e, ω_e, ω_ex_e, and B_e were obtained, and potential energy curves were calculated for the low energy Ω states of UH. The calculated adiabatic electron affinity is 0.468 eV in excellent agreement with an experimental value of 0.462 ± 0.013 eV. The lowest vertical detachment energy was predicted to be 0.506 eV for the ground state, and the adiabatic ionization energy (IE) is predicted to be 6.116 eV. The bond dissociation energy (BDE) and heat of formation values of UH were obtained using the IE calculated at the Feller-Peterson-Dixon level. For UH, UH^-, and UH⁺, the BDEs were predicted to be 225.5, 197.9, and 235.5 kJ/mol, respectively. The BDE for UH is predicted to be ∼20% lower in energy than that for ThH. The analysis of the natural bond orbitals shows a significant U⁺H^- ionic component in the bond of UH.

Molecular Properties of Thorium Hydrides: Electron Affinities and Thermochemistry

High-level electronic structure calculations of the ground and low-lying energy electronic states for ThH_x and ThH_x^- for x = 2-5 are reported and compared to available anion photoelectron detachment experiments. The adiabatic electron affinities (EAs) are predicted to be 0.82, 0.88, 0.51, and 2.36 eV for x = 2 to 5, respectively, at the Feller-Peterson-Dixon (FPD) level. The vertical detachment energies (VDEs) are predicted to be 0.84, 0.88, 0.81, and 4.38 eV for x = 2-5, respectively. The corresponding experimental VDEs are 0.871 eV for x = 2, 0.88 eV for x = 3, and 4.09 eV for x = 5. As for ThH, there is a significant spin-orbit (SO) correction for the EA of ThH₂, and this correction decreases substantially for x > 2. The observed ThH₂^- photoelectron spectrum has many transitions as predicted at the CASPT2-SO level. The FPD bond dissociation energies (BDEs) increase from 67 to 75 kcal/mol for x = 2 to x = 4 at the FPD level. The BDE for ThH₅ is much lower as it is a complex of H₂ with ThH₃. The hydride affinities for x = 2 to 4 are all comparable and near 70 kcal/mol. A natural bond orbital analysis is consistent with a significant Th⁺-H^- ionic contribution to the Th-H bonds. There is very little participation of the 5f orbitals in the bonding and the valence electrons on the Th are dominated by 7s and 6d for the neutrals and anions except for ThH₂^- where there is a significant contribution from the 7p.

Interaction of Th with H0/-/+: Combined Experimental and Theoretical Thermodynamic Properties

High-level electronic structure calculations of the low-lying energy electronic states for ThH, ThH^-, and ThH⁺ are reported and compared to experimental measurements. The inclusion of spin-orbit coupling is critical to predict the ground-state ordering as inclusion of spin-orbit switches the coupled-cluster CCSD(T) ordering of the two lowest energy states for ThH and ThH⁺. At the multireference spin-orbit SO-CASPT2 level, the ground states of ThH, ThH^-, and ThH⁺ are predicted to be the ²Δ_3/2, ³Φ₂, and ³Δ₁ states, respectively. The adiabatic electron affinity is calculated to be 0.820 eV, and the vertical detachment energy is calculated to be 0.832 eV in comparison to an experimental value of 0.87 ± 0.02 eV. The observed ThH^- photoelectron spectrum has many transitions, which approximately correlate with excitations of Th⁺ and/or Th. The adiabatic ionization energy of ThH including spin-orbit corrections is calculated to be 6.181 eV. The natural bond orbital results are consistent with a significant contribution of the Th⁺H^- ionic configuration to the bonding in ThH. The bond dissociation energies for ThH, ThH^-, and ThH⁺ using the Feller-Peterson-Dixon approach were calculated to be similar for all three molecules and lie between 259 and 280 kJ/mol.